Transmission regulation



May 7, 1935. s. B. WRIGHT 2,000,116

TRANSMISSION REGULATION Filed Jan. 17, 1930 Io/y Zwam/Mmmm@ [ine 12eeater Annu". "uur" '.5 y |NvENToR ATTORNEY Patented May 7, 1935 UNITEDSTATES l PATIENT OFFICE y 2,000,116 TRANSMISSION REGULATION ApplicationJanuary 17, 1930, Serial No. 421,454

4 Claims.

This invention relates to circuits for the transmission of intelligence,and more particularly to the regulation of transmission circuits inwhich attenuation varies not only with the energy level but also withthe frequency of the transmitted currents.

In long cable circuits, for instance, the attenuation is more marked forthe currents of high energy level than it is for the currents of 1o lowenergy level: accordingly, there is the undesirable result of a relativeincrease of echoes,

noise and crosstalk over speech currents.y Furthermore, this effect ofenergy level variation is greaterat the higher frequencies than it israt the lower.

The principal object, therefore, of the present invention is to producea counter effect to that found in long cable circuits, whereby theresultant attenuation will be substantially in- 29. dependent Of bothcurrent strength and frequency. It will be understood, however, from thefollowing description and discussion that the advantage of the inventionis not limited to producing such a counter effect, but may reside 25 inintroducing, for any purpose connected with the problems oftransmission, anauxiliary loss varying with both energy level andfrequency.

In general, the invention is embodied in an arrangement of auxiliaryimpedances inserted 3o in the circuit in association with thetransmission line, as will be more fully described hereinafter,reference being had to the accompanying drawing, in which:

Figure 1 shows diagrammatically a simple cir- 35 cuit arrangement forproducing, for instance, the compensating attenuation variationmentioned above;

Fig. 2 shows diagrammatically a modied arrangement for producing asimilar result; and

Fig. 3 shows in like manner an arrangement for accomplishing a similarresult in a somewhat more complicated but, in some respects, moreadvantageous manner.

With reference flrst to the details of Fig. l

`45 of the drawing, an artificial line is shown inserted in a longtransmission line and .inductively connected therewith throughtransformers T1 and Ti.y This artificial line has two series resistancesR1 and Rz, representative of any 50 suitable number of seriesresistances. These resistances have low temperature coenlcients. Inshunt across the artificial line there are shown a resistance R, acapacity C and an inductance L. The resistance R is of high temperatureco- 55 efficient and may take the form of a short, fine tungstenfilament in an evacuated bulb. If the elements C and L were omitted fromthe shunt circuit the effect of resistance R would be to cause theattenuation to decrease as the en` ergy increased; thus, there would berough compensation for the normal effect in the transmission line ofenergy level change. There would remain, however, the problem ofvariation of this effect with frequency variation. vWith the elements Cand L included and tuned to a high frequency, the effect of change ofcurrent strength of the attenuation is made more pronounced at highfrequencies than at low frequencies. Since the normal effect in longtrans'- mission circuits mentioned above is that the l5 variation ismore pronounced at the high frequencies but in the opposite direction tothe difference of effect introduced by this network, the' arrangementdisclosed in Fig. 1 will produce a resultant attenuation of the circuitsubstantially independent of bothenergy level and frequency.

Because of the reactances introduced by the artificial line, while allfrequencies will be trans-r mitted equally well with respect to currentstrength, there will be other inequalities in the transmission of theVarious frequencies. Thisv trouble may be corrected, if it assumesserious proportions, by the insertion in the transmissiony line of atransmission equalizer of any well known type, an example beingdisclosed in Fig. 1. In this case the equalizer comprises a resistance'R4, a capacity C2 and an inductance La connected across the line asindicated. A repeater may be `added kto restore the currents to thevalue which they had before passing through the artificial line and theequalizer.

For certain purposes it may be advantageous touse a differentarrangement of shunted elements in the artificial line. An arrangementwhich in some cases wouldrequire a less complex 40 transmissionequalizer than that shown in Fig. 1 is disclosed in Fig. 2 of thedrawing. The artificial line is connected into the ,transmission` linethrough transformers T1' and T2. The series' resistances are representedby R1 and R2. The 4,5 resistance Of high temperature coefficient Rcorresponds to R of Fig. 1, taking the form of a short, fine tungstenfilament in an evacuated bulb. In parallel with this resistance R thereare connected a capacity C', an inductance L' and a re- 50 sistance R3as shown. The equalizer and the repeater correspond to the elementsshown in Fig. 1.

While the arrangements of Figs. 1 and 2 will prove satisfactory in manycases, in certain other cases it may be found that the resistance of Ror R changes, as a function of temperature, too slowly to meet thecertain requirements, In such cases a quicker action may be obtainedwith the somewhat more complicated arrangement shown in Fig. 3 of thedrawing.

In Fig. 3 an artificial line is inserted in a long transmission line andinductively connected therewith through transformers T1l and T2. In thisartificial line there are shown, or indicated, a resista-nce R1" and aseries impedance Z. Provision is made for the variation of the impedanceZ with change of current strength in the transmission line. Associatedwith the input of.' transformer T1 and the impedance Z, which is thatlooking into the transformer T4 as indicated, is an arrangement ofvacuum tubes, resistances, capacities and inductances as shown.

If weak currents are being transmitted, the impedance Z will berelatively large because of the negative grid potential impressed on thevacuum tube V2 by the battery B3. Accordingly, interfering currents oflow energy level are limited to small values. If, however, speech orother strong currents, which may be represented by I, are impressed upcnthe input of the transformer T2, there is induced in the secondarywinding of that transformer an electromotive force which causes l theflow of a current z' through the tube V1 and the resistance R3. The dropin the resistance R3 due to the current i is opposed to theelectromotive force of battery B1. This current z' also flows throughthe filter L1"-C1-C2, which is designed to smooth out this current andto introduce any desired delay in the action of the circuit.

The electromotive force of battery B1 prevents the flow of current untilthe voice waves reach an amplitude which requires correction. When thecurrent i becomes great enough, it has the effect 4oV of impressing apositive potential on the grid of tube V2, and thus current is permittedto flow from battery B2 through the plate circuit of the tube. This flowof plate current reduces the impedance Z, and, as will be readilyunderstood, the

` result is a decrease of the loss through the corrector arrangement.

In order that correction may be made for the difference of effect ofenergy level change with frequency variation, the capacity C" and theinductance L" are introduced in series with the primary winding oftransformer T3 to give the desired offsetting effect. It may beadvantageous to include in series with these elements a resistance R2".The eifect of the high impedance input amplifier indicated in thedrawing ahead of the elements C, L and R2", is to limit the amount ofenergy which will be required to be drawn from the transmission line forthe operation of the vacuum tubes V1 and V2.

As is the case with the arrangement of Fig. 1 or the arrangement of Fig.2, a transmission equalizer and a repeater may be added with advantageto the circuit of Fig. 3.

While the invention has been disclosed as embodied in certain definitecircuit arrangements, it will be understood that the true scope of theinvention is not limited by such specific disclosure, but is determinedby the appended claims.

What is claimed is:

1. In a, circuit for the transmission of alternating currents, aregulating network including a resistance, a variable impedanceeffectively in series therewith, means responsive to changes in theintensity of the energy impressed on the input of said network formaking adjustment of the magnitude of said variable impedance tointroduce an auxiliary distortion tending to produce inequality betweenthe ratio of two values at the input of the network and the ratio of thecorresponding values at the output thereof, and means for varying suchcontrol in accordance with variation of the frequency of the currentsimpressed on the input of said network.

2. In a circuit for the transmission of alternating currents, aregulating network including a resistance, a variable impedanceeffectively in series therewith, means responsive to changes in theintensity of the energy impressed on the input of said network formaking adjustment of the magnitude of said variable impedance tending torender the relation between the input of the network and 'the outputthereof non-linear, and means for ance with variation of the frequencyof the currents impressed on the input of said network.

3. In a circuit for the transmission of alternat-ing currents, aregulating network including a resistance, a variable impedanceeffectively in series therewith, means responsive to changes in theintensity of the energy impressed on the input of said network formaking adjustment of the magnitude of said variable impedance tointroduce an auxiliary distortion tending to produce inequality betweenthe ratio of two values at the input of the network and the ratio of thecorresponding values at the output thereof, means for correcting suchcontrol in accordance with variation of the frequency of the currentsimpressed cn the input of said network, and means for controlling thedelay in the action of said network.

4. In a circuit for the transmission of alternating currents, aregulating network including a resistance, a variable impedanceeffectively in series therewith, means responsive to changes in theintensity of the energy impressed on the input of said network formaking adjustment of the magnitude of said variable impedance tending torender the relation between the input of the network and the outputthereof non-linear, means for correcting such control in accordance withvariation of the frequency of the currents impressed on the input ofsaid network, and means for controlling the delay in the action of saidnetwork.

SUMNER B. WRIGHT.

varying such control in accord- 1

